From putting the words "fad" and "anime" together. It means an anime or a series that gets adapted into one that starts or starts up a quick and high popularity. TV Tokyo had aired some of these kinds of anime starting in Japan.

Fadime

Medabots - Oriinally started out as a video game. It was adapted into a two season anime with the same name and a sequal anime, Medabots Spirit. They revolve around customizable robots with A.I.(Artificial Intelligence). It's one of my favorite anime.

Beyblade - Adapted from a Manga about spinning tops. Created by Takao Aoki, which his work is mostly around toys and games.

Bakugan - An anime series that's produced by TMS Entertainment and Japan Vistec and directed by Director Mitsuo Hashimoto. It's adapted into a strategy game with the same name by Sega and Spin Master.